It is known to use electric heating devices for mobile applications, such as for example in a motor vehicle. There is an increasing demand for suitable electric heating devices in particular in relation to an increasing use of electrically driven vehicles. In the past, so-called PTC heating elements were predominantly used as electric heating devices for mobile applications of this type and said PTC heating elements were operated at the relatively low supply voltages that are present in the onboard electrical supply system of a conventional motor vehicle that comprises an internal combustion engine. There is a demand, particularly in the case of modern vehicles that are completely or in part electrically driven, for it to be possible to also drive the vehicle in an electric manner using the supply voltages that are present in a high voltage onboard electrical supply system that is provided in said vehicles, for example using a voltage in the range between 150 volt and 900 volt. Where appropriate, voltages up to in excess of 1000 volts are even possible.
The term a ‘heating device for mobile applications’ is understood to mean in the present context a heating device that is designed for use in mobile applications and is configured accordingly. This means in particular that such a heating device is transportable (where appropriate is fixedly installed in a vehicle or is merely accommodated in a vehicle for transportation purposes) and is not configured exclusively for a permanent, non-mobile application, such as by way of example in the case of a heating system in a building. The heating device can also be fixedly installed in a vehicle (land-borne vehicle, ship, etc.), in particular in a land-borne vehicle. Said heating device can be configured in particular for heating the interior compartment of a vehicle, such as by way of example of a land-borne, water-borne or air-borne vehicle and also for heating a space that is open in part, as is to be found by way of example on board ships, in particular yachts. The heating device can also be used temporarily in non-mobile applications, such as by way of example in large tents, containers (for example site trailers), etc. In particular, the electric heating device can be configured for mobile applications as a pre-heater or auxiliary heater for a land-borne vehicle, such as by way of example for a caravan, mobile home, a bus, a passenger car, etc.
WO 2013/186106 A1 describes an electric heating device for a motor vehicle having a heat resistor that is configured as a conductor track on a substrate. The conductor track is configured to be bifilar and a widened insulation region is provided in the region where a conductor track is deflected into the opposite direction. The widened insulating region is to render it possible to adjust a current flow as far as possible through the full width of the conductor track in order to be able to avoid the formation of locally inner-lying regions that have a particularly good through-flow characteristic and regions that lie in the outer-lying edge region of the conductor track and have a poor through-flow characteristic. Although characteristics that are to a certain extent satisfactory have been achieved with the described heating device, it has been established that in the region where the conductor track is deflected temperatures occur that are still greatly increased in comparison to the temperatures in the rest of the electric heating device.